This invention relates generally to electric lamps, and particularly to those for use on motor vehicles such as, typically, headlamps. Still more particularly, the invention pertains to improvements in aiming mechanisms for aiming and retaining headlamps or the like in the proper position with respect to the vehicle.
Vehicle headlamps are being manufactured with great diversity in shape and size to suit the particular motor vehicle for which they are intended, from both esthetic and utilitarian points of view. Among the most popular of headlamp shapes is a horizontally elongated rectangle. A headlamp of this design comprises a lamp unit of horizontally elongated rectangular shape, as seen in a front view, a mounting ring of matching shape upon which the lamp unit is mounted, and a retaining ring holding the lamp unit against the mounting ring.
It has also been widely practiced to equip such a headlamp with an aiming mechanism for aiming and retaining the headlamp in the proper angular position, both vertically and horizontally, relative to the vehicle. A typical aiming mechanism comprises a helical tension spring and two aiming screws. The tension spring is engaged with the mounting ring at or adjacent one of its bottom corners for biasing the mounting ring toward the vehicle. The first of the two aiming screws extends between one shorter side, away from said one corner, of the mounting ring and the vehicle. The second aiming screw extend between the top side of the mounting ring and the vehicle.
Thus, with the tightening or loosening of the first aiming screw, the mounting ring is tilted with the lamp unit about a line that extends through the tension spring and the second aiming screw in a plane at right angles with the lamp axis, so that the lamp unit is aimed substantially horizontally. The manipulation of the second aiming screw results in the tilting of the lamp unit approximately vertically about another line extending through the tension spring and the first aiming screw in the same plane as above.
A problem has been encountered with the aiming mechanisms of the foregoing construction as applied to a vehicle headlamp of horizontally elongated, rectangular shape. Both horizontal and vertical aiming screws are tightened against the force of the tension spring. Consequently, the force required for tightening the horizontal aiming screw is inversely proportional to the perpendicular distance from that screw to the noted line extending through the tension spring and the vertical aiming screw. The force required for tightening the vertical aiming screw is similarly inversely proportional to the perpendicular distance from that screw to the noted line extending through the tension spring and the horizontal aiming screw.
However, because of the horizontally elongated shape of the lamp unit, and therefore of the mounting ring, the two distances in question have so far been not alike, and neither have been the forces required for tightening the two screws. The vertical aiming screw has been harder to tighten than the horizontal. The greater force exerted on the vertical aiming screw has often resulted in the destruction of its head.